Hand Contact vs Wheel Acceleration: Differences in Propulsion Phase Detection in Manual Wheelchair Users

(1) Background: Accurate detection of propulsion and recovery phases is essential for assessing wheelchair propulsion biomechanics. Different measurement approaches rely on distinct biomechanical signals and may therefore yield systematically different phase durations. (2) Methods: This study compared propulsion and recovery phase durations obtained from a wheel acceleration-based approach (Approach 1: marker-based motion capture) and a hand-acceleration-based approach (Approach 2: hand-mounted IMU using the continuous wavelet transform, CWT) in 33 manual wheelchair users with neurological conditions across three propulsion speeds (slow, preferred, fast). (3) Results: Approach 2 detected longer propulsion phases (bias: +0.13 s, limits of agreement (LoA) ± 0.30 s) and shorter recovery phases (bias: -0.13 s, LoA ± 0.30 s) than Approach 1. Both biases varied with speed conditions and diminished as propulsion speed increased. The later end event detected by Approach 2 is compatible with the hypothesis that hand-pushrim contact can continue after wheel acceleration changes, potentially including non-propulsive contact late in the push phase. However, this mechanism was not directly verified: no independent pushrim-force or hand-contact reference was collected. (4) Conclusions: The two approaches operationalize propulsion phase timing using different signals and should not be assumed to identify identical events. The observed differences limit direct comparison of propulsion parameters across studies unless the measurement approach is reported.